Method of oxidizing electrode structure



Nov. 12, 1935.

s. F. ESSIG 2,020,305

METHOD OF OXIDIZING ELECTRODE STRUCTURE Filed July 30, 1932 INVENTO/E San aail'l'l'sszy 1 TTOE'NEK Patented Nov. 12, 1935 PATENT OFFICE METHOD OF OXIDIZING ELECTRODE STRUCTURE Sanford F. Essig, Philadelphia, Pa., assignor to Radio Corporation of America, a corporation of ware pplication July 30, 1932, Serial No, 626,532 7 Claims. (Cl. 250-275) My invention relates to improvements in methods and apparatus for oxidizing electrode structure and, more particularly, to such structure of the mosaic type forming part of a cathode ray tube for television transmission purposes.

An important piece of apparatus for television transmission purposes is constituted by a cathode ray tube provided with a mosaic screen upon which an image of an object is projected and which is scanned by a cathode ray. The mosaic screen comprises a large number of spaced elements, each photosensitive and each capable of storing an electrostatic charge The values of the respective charges stored up during any picture frame period by the individual elements correspond to the light intensity on the respective elemental areas during that picture frame period. As the cathode ray scans the screen, the charges are discharged and utilized in a suitable circuit to develop the picture signals.

Many problems have been encountered in the development of cathode ray transmitting tubes, and one of these resided in the construction of a satisfactory mosaic screen structure, a number of different forms of which have been proposed. One form, with which satisfactory results have been obtained, comprises a relatively thin sheet of mica upon which minute silver globules are formed, closely spaced over the surface. The exposed surfaces of the globules are then oxidized to form a thin insulating coating, it being important that this coating be of the proper thickness to obtain the maximum photosensitivity. After the oxidizing step just referred to, caesium is deposited. upon each globule to photosensitize the same.

vIn the course of making mosaic screen structure of the particular type just referred to, several difficulties have been encountered, one of which has been in the uniform oxidation of the silver globules, with the oxide layer of the proper thickness. This difliculty has been more troublesome than it might otherwise have been on account of the fact that the individual globules are insulated from each other, and the fact that the supporting sheet on which the globules are formed is of insulating material. It is therefore impossible to make direct electrical. connections with the globules, wherein each connection would correspond to the single electrical connection made, for example, to the silver cathode of a caesium photocell in oxidizing the same.

For this reason, recourse cannot be had to certain of the various oxidizing methods known in other arts. In using other methods which seemed might be satisfactory, it was found that the individual globules, at different sections of the entire screen area, were oxidized to diiferent degrees. In other words, the important characteristic of oxidation of each globule to substan- 6 tially the same degree was not obtained.

In attempting to solve the problem referred to,

it was proposed to support within the tube an internal electrode in the form of a grid of fine wires disposed in close proximity to the mosaic 10 screen and in a plane parallel thereto on the side thereof containing the silver globules. Oxygen was admitted into the tube to a proper pressure, and then an ionizing discharge was established between the grid of fine wires and some other 16 part of the tube such as the electron gun for developing the cathode ray. In this method, the ions formed by collision .of free electrons with the oxygen molecules in the space between the gun and the grid pass through the grid under 20 their own inertia and strike the sflver globules, forming thereon the oxide layer. It was found, however, that it is practically impossible to obtain the desired uniform oxidation of the individual globules by between the internal electrodes. Even assuming that the electrostatic field between the internal electrodes be uniform over the entire area, the mosaic construction operates to distort this field to prevent uniform oxidation of the globules. Furthermore, after the auxiliary internal electrode or grid has served its purpose in the oxidizing step, it cannot be removed. This grid, it will therefore be understood, later serves no useful purpose in the normal use of the tube in transmitting an object, but, on the contrary, appears in the reproduced image at the receiving station.

With the foregoing in mind, it is one of the objects of my invention to provide an improved method wherein mosaic screen structure of the character referred to can be provided with a uniform oxide coating over the silver globules, the coating being of the required thickness, and without incurring the various disadvantages of the methods proposed heretofore, such, for example, as the employment of an auxiliary grid which interferes later with normal use of the tube.

Other objects and advantages will appear.

In accordance with my invention, oxidation of the globules is accomplished while keeping the cathode ray tube electrically isolated. That is, there are no metallic connections or current 55 hereinafter 50 causing an electrostatic charge 25 conductive paths between any'part of the tube structure and ground.

Whenmyinventlonispracticedinthemaking ofthetube,thesameismeehanicallycomplete except for the oxidation'and photosensitisingof thesilver globulesonthescr'een'structurebut thetubeisstillconnectedtothevacuumpmnp line. After evacuation, the connection between thetubeandthevacuumsystemiscutoiibya suitable valve device, and oxygen is admitted into formcoatofpaintoverasm'facebytheuseofa.

brush or spray.

My invention resides in the improved method and apparatus of the character hereinafter dc scribed and claimed.

For the purpose of illustrating my invention, an embodiment thereof is shown in the drawing, wherein the figure is a diagrammatic view of a system embodying my invention and by which my improved method can be carried out.

In the drawing, the reference numeral ll designates a cathode ray transmitting tube comprising a gun I! at the small end for developing and directing a ray of electrons at mosaic screen structure It set in a metallic frame it. The tube It is electrically isolated, and is supported on a suitable insulating block 20. The usual wires 22, for making connections with the various parts comprising the gun II, are shown as being free, to better illustrate and emphasise the fact that the tube II has no conductive connections at any point with groimd. The tube II is shownatthatstageinthemakingthereof whereat the samehasbeenevacuatedtoahish degree and is still connected with the glass tubular connection 24 from the vacuum pump or system (not shown). A glass tubular connection leads from a suitable oxygen supply (not shown) and is placed in communication with the interior of the tube II by turning a suitable three-way valve 28, subsequenttothetime thetubeisdlsconnected from the vacuum line N.

The screen structure It is of the type comv prising an insulating base member, such as a sheet of mica, on one side of which are minute silver globules uniformly spaced over the surface, each globule to be provided with a silver oxide layer over which there is to be later applied a layer of caesium or other photosensitive material.

In the drawing, the tube is complete except for the fact that it is still connected to the vacuum system, and the fact that the oxidizing and photosensitizing steps have not been performed.

In carrying out my improved method, the

valve 28 is first turned to disconnect the tube from the vacuum line 24, and to admit oxygen into the tube by way of the connection 20 until the desired pressure is reached. Satisfactory results have been obtained by admitting oxygen into the tube until the pressure of this gas is substantially 1500 microns. This pressure is not critical in any strict sense of the word, but should be within such range that the mean free path of the electrons in the gas is long enough 'Iheactiominoneeenaa' toinsurethattheindividualelectronscanecceleratetoavelocitynmcientlyhightogive theelectronstherequiredenergytoioniaethe oxygen molecules with which they collide. When i"orthepurpoeeofsubiectingtheacreenstrue-1o .ture l|to'th einiluenceofahl8 frequencyelectrostatic field, as heretofore mentioned, I employ ametallic disc providedwithasuitable insulating handle 42 for manual manipulation, and

connectthisdiac,byaflexible coupling ",tothe l5 'outputlineflfromasuitablehighfrequencyoscillatortl. 'lheotheroutputlinelliromtheoscillator is connected to groundias shown. 'Ihe input to the oscillator 18 is supplied from an alternatingcurrent,00cyclelinel2,inwhicha20 key M is inserted. Satisfactory results have been obtained with the voltage across lines 36 and II from 1000 to 5000 volts, at a frequency of 3000 to soooknocycies.

In operation, the disc or electrode is placed 26 in close proximity to the tube II, in some such mannerasisshowninthedrawing. 'Ihekey isthencioeed. Inthisway.theregionoverthe surface of the screen It is brought under the influence of the high frequency electrostatic field, 80

to cause ionization of the gas'molecules andthe formation of a silver oxide layer over the minute silver globules. This oxidation action is evidenced to the operator by the change which takes place in the color of the screen ll. By experi- 85 ence, it is comparatively easy to ascertain when the proper amount of oxidation has taken place. With the electrode 30 in the same position, oxidation takes place at different rates over the area of the screen It. However, 'by manipulation of 40 the electrode ll, the operator is enabled to so control the intensity of the electrostatic field withrespecttothevarioussectionsofthescreen llthattheoxidiaingactioncanbemade more intense, at any particular section than at other sections of the screen. When it is observed, from the change in color of the screen, that the oxidation of any particular portion thereof has about reached the proper point, the key M is released and then tapped to close the circuit 60 intermittently, to bring the oxidising action slowly up to the proper point.

When there has been a uniform change of color over the surface of the screen II to indicate uniform oxidation over the entire surface, the valve Ilisturnedtoagainconnectthetubetotbe vacuum line 24, after which the residual oxygen ispumped outandthetubeisevaouated. The oxidised screen is then photosensitiaed in any well known manner, andthetube ll issealed off from the vacuum line.

From the foregoing, it will be seen that I have provided an improved method and apparatus for uniformly oxidizing the silver globules, forming part of a mosaic screen for television transmittingtubesandthelikaandthatincan'ying out my improved method, no metallic connections to anypartofthetubearerequlred, themeansto ,the end, which includes the electrode 30, being entirely exterior of the tube II. It will be seen, 7

therefore, that in carrying out my improved method, no parts are required which would later interfere. in any way with the normal operation of the tube in developing picture signals.

While but one embodiment of my invention has been disclosed, it will be understood that various changes might be made without departing from the spirit of my invention or the scope of the claims.

I claim as my invention:

1. The method of oxidizing electrode structure supported in a container therefor to produce over the surface of said structure a uniform oxide layer of a thickness within predetermined limits, which comprises subjecting said structure to an atmosphere of oxygen, developing an electric field between said structure and an electrode exterior of and structurally independent of said container, and moving said electrode to vary the effectiveness of the field with respect to said structure.

2. The invention set forth in claim 1 characterized in that the electric field is oscillatory in character. i

3. The method of oxidizing substantially to a definite degree the entire exposed surface of each of a plurality of minute metallic elements spaced from each other and distributed in a generally uniform manner over the surface of electrode structure in a container, which comprises subjecting said structure to an atmosphere of oxygen, developing an electric field between said structure and an electrode exterior of and structurally independent of said container, and moving said electrode to vary the intensity of said field with respect to different sections of said structure to effect the required degree of oxidation of the entire exposed surface of each element.

4. The method of oxidizing substantially to a definite degree the entire exposed surface of each of a plurality of minute metallic elements spaced from each other and distributed over the surface of electrode structure in a container, which comprises subjecting said structure to an atmosphere of oxygen, developing an electrical field between said structure and an electrode outside of and mechanically independent of the container, and moving said electrode to subject each of said elements to substantially the same degree of infiuence of said field whereby the entire exposed surface of each of said elements is oxidized to substantially the same degree.

5. The method of oxidizing the surface of each of a plurality of discrete metallic elements insulatingly carried by a backing electrode, the assembly being disposed in a container of insulating material, through the agency of a high potential source having at least one mobile terminal, which comprises providing an oxidizing atmosphere within the container in contact with the surfaces to be oxidized, establishing an electric field between the mobile terminal and the said surfaces, to thereby ionize the gas in contact therewith, and concurrently causing relative movement between said assembly and said terminal whereby the effectiveness of the electric field and the consequent ionization are controlled.

6. The method of oxidizing a surface of an electrode supported within a container of insulating material, through the agency of a high potential source having at least one mobile terminal, which comprises providing an oxidizing atmosphere within said container in contact with the surface to be oxidized, establishing an electric field between the electrode surface and the mobile terminal, and concurrently causing relative movement between said electrode and said terminal to thereby control the effectiveness of the electric field.

'7. The method set forth in claim 6 wherein the electric field is oscillatory in character.

SANFORD F. ESSIG. 

